Bedtime nightmare - removing nappy

My 2 yr 9month old has recently been potty trained (about 3 months now) but has started to remove his nappy when I put him down to bed at night. He then proceeds to wee/poo on the carpet, even through there is a potty in his room. This can go on for a couple of hours, with me putting his nappy and pj's back on, only for a few minutes later him to take them back off again.

I've tried everything I can think of, but nothing seems to work. The other thing is that he just won't take anything seriously - its all just a big joke.

We put DD's nappy on back to front then some knickers, then a vest, then another pair of knickers tucked the vest into that. Extreme? Yes. Hot? yes. Did it work? Did it fuck. Bribery was the only thing that worked with her.

Tried nappy back to front but he just pulls it down, also tried pull ups, pants over top, pants on own, letting him choose his pjs (not tried sellotape yet though!) letting him sleep with nothing on.

He knows its naughty to wee/poo on the carpet, and shouts down to tell me he's done it, but doesn't seem to understand the consequences. I've told him off, threatened him with taking stuff away, tried bribery - nothing seems to bother him grrrrrr

Dungarees with good tight button and buttonhole fastenings might stay on and frustrate his nappy removing tenedencies. Although you might have to make the buttonholes yourself, as not much you can buy is actively designed to be difficult to remove.

And at least it would develop his button management skills...

I think I would focus on protecting the carpet (could you get a washable rug or something, and put it over a plastic sheet) and rely on bribery and time to get past it. Bloody frustrating though.